Your father-in-law's son is either your brother-in-law or your husband.
A relation on your father's side of your family is called a paternal relation.
Your father's father's brother is your great uncle.
auntie
That's a relation by marriage. Your wife's father is your father-in-law.
nephew
Father
They are your biological parents.
stepmother
Mufasa is Simba's father.
The son is the maternal grandson of the mother of the father.
The English language recognizes no relationship between the parents of your father and the father of your spouse.
Father and son